US3500972A - Sintered metal brakedrum - Google Patents

Description

March 17, 1970 c. R. TALMAGE SINTERED METAL BRAKEDRUM 4 Sheets-Sheet 1 Original Filed Feb. 18, 1965 FIG. 2

54 INVENTOR.

ARLES ROBERT TALMAGE FIG. 3 52 CH mzwmkbw A 7' TOR/VE VS March 17, 1970 c. R. TALMAGE SINTERED METAL BRAKEDRUM 4 Sheets-Sheet 5 Original Filed Feb. 18, 1965 WWI! Ill

INVENTOR. CHARLES ROBERT TALMAGE fl ibanib A TTORNEVS March 17, 1970 c. R. TALMAGE 4 Sheets-Sheet 4 INVENTO CHARLES ROBERT TAL GE ATTOR NE Y5 United States Patent Int. Cl. F16d 65/10 US. Cl. 188218 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to motor vehicle brakes and more particularly to a fade resistant brakedrum and method and apparatus for making the same. The drum comprises an annulus of inner and outer ring portions of sintered metal connected by. axially and radially extending web portions. After the annulus has been sintered, a backing plate is joined thereto by a continuous weld.

This application is a continuation of application Ser. No. 433 563 filed 'eb. 18, 1965, and now abandoned.

One of the most serious and long-Standing problems in the development of the well known drum-type automotive brakes is known as drum fade. This is a condition in drum-type brakes which occurs during prolonged or severe braking when the frictionally generated heat is not dissipated rapidly enough, causing it to expand radially beyond the limit of travel of the brake shoes. In brake drums of the type comprising a ring supported at one end by a back and free at the other end, the radial expansion is usually greater at the tree end and causes a bell-mouthing effect which, in turn, causes unevenlining wear.

An object of the present invention is to provide an improved brake drum which has a high strength-to-weight ratio and improved heat dissipating structure to thereby provide a drum which is doubly resistant to drumfade.

Another object is to provide an improved ring for a brake drum of the above character which is made from metal powder with ferrous metal as a major constituent which is sintered in a powder metallurgy process to thereby provide a relatively inexpensive drum ring having improved mechanical properties such as higher tensile strength, fatigue strength and modulus of elasticity, and which may be economically treated to provide good wear resistance in addition to the aforementioned fade-resisting characteristics.

A further object is to provide an improved brake drum which is of composite construction including a sintered metal ring of the above character joined securely to a stamped sheet metal back to thereby provide a high strength, economical brake drum assembly.

Another object of the present invention is to provide an improved method and apparatus for making a ring and/or brake drum of the above character.

Other objects, features and advantages of the present invention including various details of structure. apparatus and method will be apparent from the following description of the illustrated embodiment shown in the accompanying drawings in which:

FIG. 1 is a side elevation of a brakedrum of the present invention shown attached to a conventional hub and viewed looking into the open end of the drum.

FIG. 2 is a radial section taken on the line 2-2 of FIG. 1.

FIG. 3 is a vertical section through a compacting die set illustrating one step in one method of making a brakedrum in accordance with the present invention.

3,500,972 Patented Mar. 17, 1970 FIGS. 4. 5 and 6 are vertical center sections of a modified compacting apparatus illustrating a sequence of steps in another method of making a brakedrum both in accordance with the present invention.

Referring to FIGS. 1 and 2 of the drawings, the improved automotive brakedrum of the present invention comprises an assembly of a one-piece drum ring 10 and a stamped metal back 12 secured to one end of the ring. Back 12 is provided with five holes for receiving wheel mounting bolts 14 which secure back 12 to a conventional wheel hub 16 in the usual manner.

Ring 10 is a relatively heavy walled, tubular shaped member in which is formed a plurality of holes 18 which extend parallel to the axis of the ring from one end face 20 of the ring to the other end face 22 thereof, the holes being open at their ends to permit free passage of air therethrough. As shown in FIG. 1, holes 18 are equally spaced around ring 10 and, by way of example, there is a total of 48 holes in a drum having an outside diameter of about'l 1 /2 inches. This multiplicity of axially extending passages, preferably in the form of cylindrical holes 18, may be considered for purposes of illustrative analysis to create three separate zones or structural portions in ring 10. When thus considered, there is an inner ring 24 which is a cylindrical, imperforate and integral portion of the drum ring. The smooth inner periphery of inner ring 24 forms the brake track 26 of the brake drum. The portion of the drum ring disposed radially outwardly of holes 18 forms an outer ring 28 which is also a cylindrical, imperforate and integral portion of the drum ring, outer ring 28 being concentric with inner ring 24. For some applications, the smooth outer periphery of outer ring 28 may also serve as a brake track. Inner and outer rings 24 and 28 are integrally joined by the radially and axially extending webs 30 formed one between each adjacent pair of holes 18. It is to be understood that the foregoing analysis of ring 10 into three portions, i.e., inner ring 24, outer ring 28 and a multiplicity of Webs 30, is intended merely to facilitate understanding of structural functions rather than by way of limitation.

As best seen in FIG. 2, end face 22 is axially offset inwardly of the end face 32 of inner ring 24 so that the lip of a conventional dust cover (not shown) may overlap end face 32 to cover the open end of the drum, as is well understood in the art. The face 20 of ring 10 has an annular pilot recess 40 to receive the annular mounting portion 42 of back 12.

In a preferred embodiment of the invention, back 12 is secured to end face 20 of ring 10 by a circumferentially continuous shielded arc weld 44 at the outer peripheral edge of back 12. It is to be noted that this arc welded joint has proven successful even when employed to unite a steel back 12 with a ring 10 made of sintered metal as disclosed hereinafter. In some applications using this are welded joint it is desirable to infiltrate the sintered ferrous metal with a suitable material such as copper, thereby reducing or preventing internal oxidation in the weld.

Although drum ring 10 of the present invention could be made from cast iron or other suitable material by known casting techniques, ring 10 is preferably produced in ferrous material by a powder metallurgy process in accordance with the embodiments of the method of the present invention described hereinafter. The first step in both embodiments of this method comprises the preparation of a powder mix which. by way of illustration, comprises the following proportions by weight:

Parts Iron powder 96 Copper powder (copper content can be varied) 3 Graphite l Stearate or other suitable lubricant l 3 he above-listed. ingredients in powder form are interiixed mechanically.

In the first embodiment of the method, the next step a to place the proper volume of the powder mix in a Jitable die set such as that shown schematically in FIG. This die set includes a lower annular outer die 50 fixedsupported on a suitable press bed (not shown), a cylinrical inner core die 52, and upper and lower annular ressure dies 53 and 54. Dies 50 and 52 are suitably raped and concentrically disposed to form an annular lold cavity radially therebetween which corresponds to me outer dimensions and general shape of drum ring 10 1 the fully closed position of the dies (FIG. 3). Upper ie 53 is adapted to be pressed downwardly by an asociated ram 55 of a high pressure press, and lower die 4 is similarly actuated but in the 'opposite direction. n order to fill the mold with powder mix upper die 53 is aised to permit access to the mold cavity.

After the powder mix has been poured into the mold avity, the powder is leveled with the top of dies 50 and 2. Then the loose powder is compacted by pressing die 3 downwardly and die 54 upwardly as indicated by the vrrows in FIG. 3. The powder apparent density, die comvression ratio and pressing force are selected to produce green. compact 10' having the desired density.

. After the pressing or compacting step, the die set is tpened by raising die 53 so that the resulting green comact 10 can be suitably removed from the die set.

The next step in both embodiments of the method omprises sintering the green compact 10 under normal intering conditions for obtaining pearlitic material, such LS at about 2050 ,F. in a dissociated ammonia atmosphere or one hour. This heating of the compact at an elevated emperature below the melting point of the major contituent causes the green compact to sinter into a single, trong, smooth metallic part wherein the materials are 10 longer in the form of powder, and the graphite has :ombined, resulting in a pearlite structure.

In the first embodiment of the method, after the sinered ring 10 has been cooled it is machined to its finished 'orm as shown in FIGS. 1 and 2 by suitable drilling, turnng and/ or other conventional metal Working steps. Ring is then ready for assembly, preferably with a stamped :teel back 12 which, as previously described, is are welded o the ing.

It will now be apparent that the foregoing method proliClCS a way of making the brake drum of the invention in 'errous material of uniform density and composition. 30th density and composition can be readily modified to )rovide desired changes in the resultant material proper- :ies. Also, in lieu of or supplemental to introduction in the aowder mixing step, the copper component may be intro= luced by infiltration methods as disclosed and claimed in ny copending application Ser. No. 342,158, filed Feb. 3, [964, now Patent No. 3,326,678.

The above described method may be modified in accordance with the present invention to form the multiplicity of 10168 18 simultaneously with the compacting steps by use 3f the modified compacting die set illustrated in simpliied form in FIGS. 4, and 6.

Referring to FIG. 4, the modified die set includes an annular outer die 150 supported on a press bed 151, a :ylindrical inner core 152 suitably supported concentrically within die 150, an upper annular punch 153 carried by a ram of the press (not shown), a lower annular punch 154 and a plurality of core pins 156 corresponding in number and location to holes 18 of ring 10. Pins 156 are fixed to a carrier 158 which slidably encircles the lower portion of punch 154. The upper portion 159 of punch 154 is vertically movable with a close sliding fit in the annular space or cavity of the die set defined radially between core 152 and die 150. Pins 156 extend upwardly from carrier 158, slidably through holes 160 in upper portion 159 of punch 154 and thence upwardly through the cavity of the die set. Upper punch 153 also has a. plurality 4 of holes 162 adapted to slidably receive the upper ends of pins 156. Punch 153 is adapted to be received in the die cavity. with a close sliding fit and its lower face is suitably contoured as at. 164 and 166 complemental to the finished end contour of ring 10.

As in the compact forming steps of the previously described method, the modified method comprises'the steps of pouring the powder mix 168 into the mold cavity with the die set parts positioned as shown in FIG. 4. The powder is leveled with the top of core 152 and die 150, pins 15 6 also being positioned with their upper ends fiush therewith.

As illustrated in FIG. 5, the next step of the modified method comprises compacting the loose powder 168 by forcing punch 153 downwardly into the mold cavity while simultaneously forcing punch 154 upwardly as indicated by the arrows in FIG. 5 to thereby compress the powder into the green compact 110. The upper ends of pins 156 are received in holes 162 of punch 153 as the upper and lower punches move toward one another in this compacting step.

As shown in FIG. 6, the next step in the modified method comprises ejecting compact from the mold cavity. This is accomplished by retracting punch 153 upwardly to withdraw the same from the mold cavity while simultaneously further elevating punch 154, pins 156 being held stationary by carrier 158 so that compact .110 is stripped from pins 156 as it is pushed by punch 1S4 upwardly out of the die cavity to the ejected position thereof shown in FIG. 6. It is to be understood that the compacting die set employed in the modified method is preferably provided with suitable draft: angles on core 152 and outer die as well as on the upper portions of pins 156 so that these parts can be slightly tapered to facilitate ejection of the compact from the die set. However, compact 110 at this point is essentially identical in shape and size to the finished ring 10 of FIGS. 1 and 2, holes 18 having been cored in the compacting step by pins 156.

Compact 110 is then sintered as previously described. However, the finish machining steps required subsequent to sintering the previously described method are substantially eliminated by the modified method, thereby significantly reducing the manufacturing cost of the brakedrum.

Referring to the improved product of the invention, ring 10 has a section modulus which is much greater than equal weight prior art drums which. are of relatively radially thin design. Due to the relatively large radial thickness of ring 10, it resists expansion caused by mechanical stress when brake track 26 is engaged by the brake shoes. In addition, ring 10 has a much. greater cooling surface area exposed to air due to the multiplicity of axial holes 18 which conduct air currents through the ring.

Outer ring 28 also provides additional heat transfer area and, being a full ring and being spaced radially outwardly from the brake surface 26 by the multiplicity of thin webs 30, remains relatively cool during a stop. Hence outer ring 28 also functions to circumferentially restrain inner ring 24 against its tendency to expand radially, thereby further resisting thermal expansion of the drum and resultant drum fade.

Ring 10 when made of sintered iron rather than cast iron can have a much higher tensile strength, which in turn provides a much greater resistance to fracture re sulting from extreme stress conditions such as the aforementioned differential expansion stresses. Ring 10 also provides increased resistance to stresses tending to produce distortions such as out-of-roundness and bell-mouth ing due to outer ring 28 as well as webs 30 being axially coextensive with the inner ring 24.. The cylindricalv shape of the air passage holes 18 is economical to produce, par ticularly when cored as disclosed. herein, and also results in webs 30 having an. ideal section. for compression loadi.e., each web has an hourglass shape in radial. cross section (FIG. 1) due to its cylindrical concave side walls, and each web is securely united with the inner and outer rings 24 and 28 due to the integral connection of its inner and outer radial ends with these rings. The perforated geometry of ring 10, plus its enhanced heat conductivity when copper has been infiltrated into the sintered iron, combine to provide an improved heat transfer and storage device.

Referring to the illustrated embodiment of drum ring 10, successful results have been obtained by employing dimensions as set forth below by way of illustration and not by way of limitation:

Inches Outside diameter of ring 10 11.437 Inside diameter of inner ring portion 24 9.5 Radial thickness of outer ring portion 28 .125 Diameter of holes 18 .578 Radial thickness of inner ring portion 24 .265

I claim:

1. A brakedrum comprising an annulus of sintered metal made by sintering a one piece metal powder compact having the form of the annulus as defined hereinafter, said annulus including an inner ring portion having an inner cylindrical braking surface, an outer restraining ring portion concentric with said inner ring portion, a plurality of web portions integrally connected to said ring portions and extending axially and radially intermediate said inner and outer ring portions, said web portions defining a plurality of cylindrical passages extending parallel to the axis of said drum intermediate said ring portions and being open at the opposite axial ends of said passages, and a stamped metal back disposed generally radially of the annulus and having a peripheral portion secured by a circumferentially continuous weld to an end face of said inner ring portion after said annulus has been sintered.

2. The brakedrum as set forth in claim 1 wherein the radial thickness of said inner ring portion is about twice the radial thickness of said outer ring portion and the radial thickness of each of said web portions is about twice the radial thickness of the inner ring portion.

3. The brakedrum set forth in claim 1 wherein said back is secured to said inner ring by a circumferentially continuous arc weld forming said weld.

4. The combination set forth in claim 3 wherein said end of the inner ring portion has a circumferential recess receiving said peripheral portion of said back, said weld being located at the junction of the outer periphery of said peripheral portion of said back and the adjacent surface of said end face.

5. The brakedrum as set forth in claim 1 wherein said powder compact consists primarily of ferrous powder and said back comprises sheet steel.

6. The brakedrum as set forth in claim 5 wherein said annulus of sintered metal contains infiltrated copper prior to having said back secured thereto by said weld.

7. In a brakedrum of the type having a drum ring with an inner cylindrical braking surface adapted to cooperate with brake shoes radially outwardly expansible thereagainst, the improvement characterized by said drum ring comprising an annulus constructed of sintered metal made by sintering a one-piece ferrous metal powder compact having substantially the form of the annulus as it exists in its finished form, and a steel back disposed generally radially of the annulus at one end thereof and having a peripheral portion secured by a circumferentially extending weld to a face of said annulus at said one end thereof after said annulus has been sintered.

8. The brakedrum as set forth in claim 7 wherein said powder compact consists primarily of ferrous powder and said weld extends continuously circumferentially of said peripheral portion of said back.

9. The brakedrum as set forth in claim 8 wherein said back comprises a stamped sheet steel member and said annulus of sintered metal contains infiltrated copper prior to having said back secured thereto by said weld.

References Cited UNITED STATES PATENTS 1,553,670 9/1925 Cautley 188-218 2,287,952 6/1942 Tormyn 188--218 3,343,955 9/1967 Talmage 29-420.5 X

GEORGE E. A. HALVOSA, Primary Examiner US. Cl. X.R.

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